Mad about Science: Shaving cream

By Brenden Bobby
Reader Columnist

What is this mystical substance that squirts out of a can and foams up on your face, legs, pits or bits to make shaving a breeze? How did human beings survive in a time before shaving cream? Is this stuff safe to eat?

Modern shaving cream is a detergent, though it comes with some added benefits and exclusive applications. Most shaving cream since 1949 is aerosolized and comes out of a can, foaming on contact with anything it touches and producing a fragrant chemical smell. Magically it facilitates easy hair removal anywhere you spray it while lessening the chance of you cutting and injuring yourself — but how does it do all of this?

Soap and detergent are two distinctly different compounds that fulfill the same function. First, let’s take a look at soap.

Soap was produced for thousands of years by mixing alkaline materials, such as ash from wood fires, with rendered animal fats and other oils. The substance produced by mixing these worked well when lathering and scrubbing to remove grease and grime from surfaces and cloth as well as our own bodies. People discovered they could mix herbs, flowers and other fragrances with this substance to make soap and everything it touches smell nice.

Mass production of soap-like materials is a far cry from how soap is traditionally made. The next time you’re in the bath and beauty aisle at your local store, take a quick look at labels and see what is and isn’t actually referred to as “soap.” Many mass-produced products are detergents, but not soap, as they tend to use purely artificial chemical compounds to produce something with the cleansing properties of soap for far cheaper. On paper, this sounds great. In practice, it could be a major factor as to why certain people have strong skin reactions to certain types of detergent projects but not others.

This might sound like arguing about the difference between Oreos and Hydrox cookies, but there is a distinctive difference between soap and detergent. Soap is produced by a process called “saponification,” which happens when natural fats are cleaved in a process called hydrolysis by alkali materials. Detergents are synthetic mixtures of artificially produced chemicals. In order for a product to be legally called soap on promotional packaging, the FDA specifies that it must be composed mainly of “alkali salts of fatty acids.” If you’re having skin troubles, rashes or irritation, check what you use in the shower — if it doesn’t say “soap” anywhere on the package, there’s a chance you’re having a reaction to synthetic detergents.

Whether shaving cream is considered a soap or a detergent depends on the brand. Most canned-based creams are synthetic detergents. Shaving cream fills a special niche within the cleaning world — it doesn’t act as a simple degreaser for breaking up grease and grime. Shaving cream is designed to act as a hydrating lubricant that creates a layer between your skin and the edge of a razor while simultaneously hydrating the hair you’re trying to shave. This layer helps the blade glide across the surface of your skin without digging in as easily while simultaneously slicing through hair.

However, this isn’t the only use for shaving cream. Being a fairly powerful detergent, did you know you can use it as a low-cost cleaning agent as well? The foamy nature of shaving cream delivers volume when applied to something like a stain on a countertop. It works shockingly well to clean flat surfaces like counters, tabletops or the external surface of your toilet tank. It also doesn’t require much elbow grease to activate as opposed to liquid soaps.

One major drawback of shaving cream when used for cleaning spills is its nature to act as a hydrator for your skin. This allows for a rapid transfer of some chemical substances if you’re cleaning with your bare hands to your skin — dyes and food coloring in particular rapidly stain your skin when used this way.

You may be wondering how the substance foams up when squirted from a bottle. The substance is compressed into the can and pressurized with butane gas. When you press down on the cap to release the valve you open a channel between the pressurized can and the outside air. Gas will always work to equalize pressure, so the high pressure of the butane in the can will rush out and carry some of the soap or detergent with it. The gas rushing through the compound will create bubbles and create the foam — simple as that. Butane is extremely flammable, so if the integrity of the can is compromised due to heat, the equalization of pressure will be an explosive event.

One very fun application for shaving cream is to create paper marbling. This is an art form that dates back to at least the 16th century. Artists would suspend paint and pigment in oils and swirl them around with the base of a brush to create wild patterns. They would proceed to dip the surface of something like a book jacket into the oil and allow the paints to transfer the pattern onto the paper, which would remain after the oil was drained. 

You can actually perform this with shaving cream, food coloring dye or water-based paints on a sheet of printer paper. Just be sure to have a sharp paint scraper to wipe off the foam once the color has soaked into the page.

This is a fun activity you can do in fewer than five minutes with your family to create psychedelic artwork that is truly unique — due to the capillary action of the paper, you will never be able to perfectly duplicate any one piece of art you create with this method.

Stay curious, 7B.